<!DOCTYPE html>
<html>
<head>
	<title>css 绘制一个圆</title>
	<style type="text/css">
		.circle {
			border-radius: 50%;
			width: 4rem;
			height: 4rem;
			background: #333;
		}
	</style>
</head>
<body>
	<div class="circle"></div>
</body>
</html>